1. Field of the Invention
The present invention relates to systems and methods for aligning instrument boresights, and in particular to a system and method for aligning a dish antenna boresight.
2. Description of the Related Art
Conventional systems and methods of satellite dish alignment require that a user approximate the pointing direction of the antenna from external sightings or a magnetic compass and then search for an antenna signal null. This process must be repeated until an adequate pointing accuracy is achieved.
For example, the antenna alignment method employed by satellite broadcasters such as DirecTV(trademark), typical of conventional methods, requires approximate alignment of the antenna toward the satellite based on estimated directions depending upon the user""s location on the Earth. Fine alignment of the antenna, e.g. within 0.1xc2x0, is then achieved in conjunction with the receiver/decoder of the system based upon maximizing the strength of the received signal. However, strength of the received signal may not be an accurate indicator of the satellite direction. Furthermore, it is very difficult to align a receiving antenna to a broadband antenna with a narrow beamwidth as the margin for error is very small; physical manipulation of the antenna often results in overshooting the intended position.
In addition, the conventional systems and methods will not acquire a mean position if the transmitting antenna is moving, such as with systems based upon high-altitude platforms or non-geostationary satellites.
Gyrocompassing methods have also been used to align instrument boresights as described in U.S. Pat. No. 5,272,922, issued Dec. 28, 1993, which is hereby incorporated by reference. However, such systems are very complex and expensive.
There is a need in the art for systems and methods for simple, accurate and inexpensive instrument alignment without the attendant difficulties described above. There is further a need for self-contained systems and methods of instrument alignment. There is still further a need for systems and methods for aligning instruments to a station position (satellite or other) whose apparent position is not stationary over time, or whose signal may not be present at the time of alignment.
The present invention satisfies these needs.
To address the requirements described above, the present invention discloses apparatuses and methods for determining an instrument boresight heading which can be used in aligning an antenna with respect to Earth coordinates.
One embodiment of the invention comprises an instrument having a boresight, an elevation positioner for positioning the elevation of the instrument boresight having an elevation axis, an azimuth positioner for positioning the azimuth of the instrument boresight having an azimuth axis and a sensor including a gyro having a sensitive axis.
One method of the invention comprises recording a first output of a gyro of an azimuth positioner having an instrument boresight azimuth heading in a first position, rotating the azimuth positioner to a second position, recording a second output of the gyro and rotating the azimuth positioner to a third position, recording a third output of the gyro and determining the azimuth heading relative to true north from the first, second and third output.
The foregoing allows simple, accurate alignment of antennas based upon a local vertical direction and the direction of the Earth""s rotation.